NOTE: If you use one of these programs, DO NOT LOSE YOUR DATAFILE or the PASSPHRASE to unlock it or you are really screwed.
So...what do you do...WRITE IT DOWN???
Many people actually do suggest that you write it down and put it in your wallet. Personally, I wouldn't do that. It's an important bit of information. Think about it and come up with something that is both memorable to you, and as hard as possible for someone else to guess. Wait a couple of days. If you can still remember it, use it. If not, come up with something else. Once you've got a good key, you can start using it. :-)